Movies forced to do double duty as thoughtful entertainment and public-service campaign (like last year’s sex trafficking fiasco, “Trade of Innocents”) are almost invariably irritating. Audiences rarely want to be lectured to, and hardworking single mothers — those with time to visit a movie theater, that is — are unlikely to be thrilled when their representative in “Hello Herman” learns that prioritizing her career might have helped turn her teenage son into a mass killer.

That said, this well-meaning adaptation of John Buffalo Mailer’s 2001 play is more redundant than offensive. Focusing on Herman (Garrett Backstrom, excellent), a relentlessly bullied 16-year-old who slaughters dozens of classmates and several adults, the story scoops all the usual suspects — ultraviolent video games, the Internet, a broken home — into a random ball of blame. Hoping to untangle it is a left-wing blogger laughably named Lax Morales (Norman Reedus, more relaxed laying waste to zombies in “The Walking Dead”), whose jailhouse interviews with Herman form the core of the film. Haunted by his experiences while infiltrating a nest of white supremacists, Lax may be even more troubled than his young interviewee.

Pointing at everything and elucidating nothing, “Hello Herman” arrives freighted with the anti-bullying agenda of its director, Michelle Danner. Unlike Gus Van Sant, whose “Elephant” responded to the Columbine High School massacre with wondering distance and humility, Mr. Mailer wants culprits and closure. Watching his frantic attempts to explain the inexplicable, I was reminded of Michael Moore’s “Bowling for Columbine,” when he asks the musician Marilyn Manson what he would say to the Columbine killers.